The present invention relates to mammalian galanin receptors. More particularly, it relates to rat and human galanin receptors, isolated nucleic acids and recombinant vectors encoding the receptors, methods for making the receptors, fragments or fusion proteins thereof using recombinant DNA methodology or chemical synthesis, and to methods for using the receptors in screening systems to identify inhibitors for the treatment of various diseases. This invention further relates to antibodies, both polyclonal and monoclonal, which specifically bind to the galanin receptors or to anti-idiotypic antibodies against them, and to fragments and fusion proteins thereof.
Galanin is a polypeptide found in the central and peripheral nervous systems which regulates multiple processes such as endocrine and exocrine pancreatic secretions, intestinal motility, and modulation of behavioral, cognitive, and sensory functions such as feeding, learning, memory and nociception. See, e.g., Merchenthaler et al., Prog. Neurobiol. 40:711-769 (1993), and Hxc3x6kfelt et al. in Galanin: A New Multifunctional Peptide in the Neuro-Endocrine System, Wenner-Gren International Symposium Series, 1991, Vol. 58, MacMillan, Cambridge, U.K. Because of its wide distribution and multiple activities, Galanin is believed to be involved in a number of medical conditions, including obesity, Alzheimer""s disease, nociception, dementia, eating disorders, diabetes, dislipoproteinemia, developmental disorders of the neural systems, disorders of the digestive systems, growth disorders, sexual and reproductive dysfunctions, stomach ulcers, sleep disorders, and regeneration of injured neuronal systems.
The physiological effects of galanin are mediated by specific receptors in target tissues. One such receptor from insulin-secreting cells has been described by Lagny-Pourmir et al. [Endocrinology 124:2635-2641 (1989)]. Human galanin receptors have been cloned by Habert-Ortoli et al. [Proc. Natl. Acad. Sci. USA 91:9780-9783 (1994)], Hinuma et al. [European Patent Application Publication EP 0 711 830 A2] and Amiranoff et al. [International Patent Application Publication No. WO 95/22608].
In view of the important role of galanin in many physiological processes and medical conditions, there is a need for materials and methods for identifying selective agonists and antagonists of galanin.
The present invention fills the foregoing need by providing such materials and methods. More particularly, this invention provides novel mammalian galanin receptors, isolated or recombinant nucleic acids encoding the receptors, and recombinant vectors and host cells comprising such nucleic acids.
The isolated or recombinant nucleic acids are selected from the group consisting of:
(a) a nucleic acid encoding a mammalian galanin receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a subsequence thereof;
(b) a nucleic acid that hybridizes under moderately stringent conditions to the nucleic acid of (a) and encodes a polypeptide that (i) binds galanin and (ii) is at least 80% identical to a receptor encoded by the nucleic acid of (a); and
(c) a nucleic acid that, due to the degeneracy of the genetic code, encodes a mammalian galanin receptor encoded by a nucleic acid of (a) or (b).
This invention further provides methods for making the galanin receptors comprising culturing a host cell comprising a nucleic acid encoding a mammalian galanin receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a subsequence thereof, under conditions in which the nucleic acid is expressed. In some embodiments, the method further comprises isolation of the receptor from the culture.
This invention also provides polypeptides comprising a fragment of a mammalian galanin receptor having an amino acid sequence corresponding to the sequence of at least about 8 contiguous residues of the complete receptor sequence. Preferably, the polypeptides comprise at least about 12, more preferably at least about 20, and most preferably at least about 30 such residues.
Still further, this invention provides fusion proteins comprising a mammalian galanin receptor or a polypeptide therefrom covalently linked to a fusion partner.
The present invention also provides antibodies, both polyclonal and monoclonal, that specifically bind to one or more of the galanin receptors or to polypeptides therefrom, and anti-idiotypic antibodies, both monoclonal and polyclonal, which specifically bind to the foregoing antibodies.
This invention further provides a method for producing a mammalian galanin receptor comprising culturing a host cell comprising a nucleic acid encoding a mammalian galanin receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a subsequence thereof, under conditions in which the nucleic acid is expressed. In one embodiment the receptor is isolated from the culture.
This invention still further provides a method for treating galanin-mediated medical conditions comprising administering to a mammal afflicted with a medical condition caused or mediated by galanin, an effective amount of an antibody, or an antigen-binding fragment thereof, that specifically binds to a mammalian galanin receptor having an amino acid sequence defined by SEQ ID NO: 4, or a subsequence thereof, and pharmaceutical compositions comprising one or more of such antibodies or fragments and a pharmaceutically acceptable carrier. Preferably, the mammal is a human being.
The present invention also provides a method for identifying a galanin agonist or antagonist comprising:
(a) contacting a mammalian galanin receptor having an amino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a subsequence thereof, in the presence of a known amount of labeled galanin with a sample to be tested for the presence of a galanin agonist or antagonist; and
(b) measuring the amount of labeled galanin specifically bound to the receptor;
whereby a galanin agonist or antagonist in the sample is identified by measuring substantially reduced binding of the labeled galanin to the galanin receptor, compared to what would be measured in the absence of such agonist or antagonist.
In a preferred embodiment, membranes isolated from mammalian cells comprising a nucleic acid encoding the galanin receptor are used as the source of the receptor.